Engine spark plug grounding structure, grounding wiring apparatus, and grounding wiring method

ABSTRACT

A grounding member made of a spring steel includes a hexagonal top with a through hole, contact pieces extending from straight sides of the hexagonal top, and a grounding strip brazed to one of the contact pieces. The grounding member attaches to a spark plug with a spark plug insulator passing through the through-hole. The contact pieces pressure contact a peripheral surface of a hexagonal nut of the spark plug. A grounding wire is connected to a negative electrode of a battery. Electric charges generated in a spark gap are returned to the battery negative electrode from an external electrode of the spark plug via a spark plug housing, the grounding member, and the grounding wire. If the spark plug is loosely fitted in an engine cylinder head, or even if some engine body components are aged, electric charges flow without problems, preventing reduction of discharging performance.

FIELD OF THE INVENTION

The present invention relates to a grounding structure for a spark plugof an engine driven by fuel such as gasoline or liquefied petroleum gas(LPG), a ground wiring device, and a method of wiring the groundingstructure.

BACKGROUND OF THE INVENTION

Usually, in an engine driven by gasoline, liquefied petroleum gas or thelike, the compressed air-fuel mixture is fired by electric sparksgenerated by an ignition system. The ignition system is either acontacting type (electric type) or non-contacting type (electronictype), and generates electric sparks using a spark plug in response tohigh pressure applied from an ignition coil, thereby firing the air-fuelmixture.

FIG. 7( a) of the accompanying drawings shows an external appearance ofa spark plug 10, and FIG. 7( b) is a cross section of the spark pluginstalled in a cylinder head H of an engine with inner parts.

Referring to those figures, the spark plug 10 includes a centerelectrode 2 axially housed in a cylindrical insulator 1. The centerelectrode 2 has one end sticking out via a bottom opening of theinsulator 1. High pressure is generated by the ignition coil betweenpositive and negative electrodes of a battery (not shown), and isapplied between the sticking-out end of the center electrode 2 and toone end of an external electrode 3.

A lower half of the insulator 1 is enclosed in a spark plug housing 4,of which lower peripheral surface is a male-screwed part 4 b. The sparkplug 10 is fitted into a cylinder head H of the engine via themale-screwed part 4 b. The lower end of the center electrode 2 comes outvia a bottom opening of the male-screwed part 4 b. The externalelectrode 3 is attached around a lower periphery of the male-screwedpart 4 b, and has its end facing with the lower end of the centerelectrode 2. Discharges are caused in a spark gap G between the end ofthe external electrode 3 and the end of the center electrode 2. Thespark gap G faces with a combustion chamber of the engine.

An upper end of the center electrode 2 is connected to a terminal nut 5fixedly fitted in an upper opening of the insulator 1. A high pressurecord C extends from an ignition coil connected to the positive electrodeof the battery, and is connected to the terminal nut 5 via a cap 6.

Electric charges emitted in the spark plug gap G return to the negativeelectrode 11 of the battery from the external electrode 3 via the sparkplug housing 4, the cylinder head H of the engine, an engine body, achassis of the vehicle where the engine body is mounted, and so on. Theelectric charges tend to sluggishly flow while they pass over a longrange through a number of contacts, engine body, chassis and so on.

Further, sometimes the spark plug 10 is loosely attached in the cylinderhead H (i.e. at the male-screwed part 4 b of the spark plug housing 4),or there are poor conductions caused by aged components of the enginebody. In such a case, electric charges tend to flow non-smoothly, whichwill worsen the discharge performance. The lower the dischargeperformance, the weaker firing force, and the lower fuel efficiency.Further, engine torque characteristics will be worsened.

In the former case, the spark plug 10 is vibrated each time sparks aregenerated in order to fire the air-fuel mixture, so that the connectionbecomes slack between the spark plug 10 and the cylinder head H. In thelatter case, engine components are always exposed to intense heat, andwill be inevitably aged.

The invention has been contemplated in order to overcome problems of therelated art, and to provide a grounding structure which can removefactors causing reduced discharge performance, enable electric chargesto be effectively returned to a negative electrode of the battery, andto improve the fuel efficiency and engine torque characteristics.

SUMMARY OF THE INVENTION

In order to accomplish the foregoing object, the invention proposes agrounding member which is attached to a spark plug housing, and isconnected to a negative electrode of a battery using a grounding wire.

The grounding member enables electric charges generated by dischargingto return to the negative electrode of the battery from the spark plughousing via the grounding wire. Even if the spark plug happens to beloosely attached to the engine body, or even if some engine componentsare aged, the electric charges can flow without any inconvenience, whichis effective in preventing the discharge performance from being lowered.The thermal efficiency of the engine at the time of ignition can beimproved, and fuel efficiency and torque characteristics will be betterthan those of the related art.

The grounding member is shaped to be engagebale with or disengagebalefrom a hexagonal nut of the spark plug housing, and can be easilyattached to and detached from the spark plug only by removing a cap of ahigh pressure cord without using a special tool or skill.

The grounding member includes a hexagonal top of which size and shapeare substantially identical to those of the hexagonal nut of the sparkplug housing. The hexagonal top has a through-hole at the centerthereof, and contact pieces extending from the six straight sidesthereof. When attached onto the hexagonal nut, the grounding member hasits contact pieces brought into pressure contact with the peripheralsurface of the hexagonal nut due to resiliency.

Alternatively, the hexagonal top may have a through-hole at the centerthereof, and three contact pieces extending from every two straightsides thereof. When attached onto the hexagonal nut, the groundingmember has its contact pieces brought into pressure contact with theperipheral surface of the hexagonal nut due to resiliency.

The grounding member preferably has contact pieces in contact with theperipheral surface of the hexagonal nut, a through-hole via which aninsulator of the spark plug passes, and a grounding strip sticking outof an engine cylinder head.

Therefore, the grounding member can be attached to the spark plug whichhas been installed in the engine cylinder head. In this state, theinsulator passes through the through-hole of the grounding member, andthe contact pieces extend over the hexagonal nut of the spark plughousing, and are in pressure contact with the peripheral surface of thehexagonal nut.

Some spark plug is deeply embedded in the cylinder head. In such a case,the grounding member has the grounding strip extending out of the enginecylinder head, which facilitates the connection between the groundingstrip and the grounding wire.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) shows an external appearance of a spark plug with a groundingmember attached thereto in one embodiment of the invention.

FIG. 1( b) is a cross section of the spark plug.

FIG. 2 is a perspective view of the grounding member of the firstembodiment.

FIG. 3 is a cross section of a modified example of the embodiment.

FIG. 4 is a perspective view of a further grounding member.

FIG. 5 shows a top plan view, a side elevation, and a front sectionalviews of the grounding member of FIG. 4.

FIG. 6( a) schematically shows patterns for punching a metal plate tomake grounding members each having three contact pieces.

FIG. 6( b) schematically shows patterns for punching a metal plate tomake grounding members each having six contact pieces.

FIG. 7( a) shows an external appearance of an existing spark plug.

FIG. 7( b) is a cross section of the spark plug of FIG. 7( a), withinternal components mounted.

BEST MODE FOR EMBODYING THE INVENTION

The invention will be described with reference to one embodiment shownin the drawings.

In the drawing figures, like or corresponding parts are denoted by likeor corresponding reference numerals to those shown in FIG. 7( a) andFIG. 7( b).

A spark plug 10 is configured and is attached to an engine cylinder headH similarly to the spark plug shown in FIGS. 7( a) and 7(b), and willnot be described here. FIG. 2 shows a grounding member 20 attached tothe spark plug 10 in the embodiment.

The grounding member 20 is made of spring steel, and includes ahexagonal top 21 in the shape of a cap, and a grounding strip 22 asshown in FIG. 2. The hexagonal top 21 has six rectangular contact pieces23 (called the “contact pieces”) extending from the six straight sidesthereof. The grounding strip 22 is brazed onto one of the contact pieces23. Adjacent contact pieces 23 are spaced from each other. The sixcontact pieces 23 are radially extendable due to their resiliency andthe spaces therebetween. The hexagonal top 21 has a perfectly circularthrough-hole 24 at the center, and is fitted onto a hexagonal nut 7 ofthe spark plug 10 from above an upper end of an insulator 1, so that thecontact pieces 23 come into pressure contact with the peripheral surfaceof the hexagonal nut 7. In this state, the insulator 1 extends throughthe circular through-hole 24 of the cap-shaped body 21.

The grounding strip 22 is brazed onto one of the contact pieces 23, andstands upright. Referring to FIG. 1( b), the grounding strip 22 sticksout of the cylinder head H.

The grounding member 20 is attached to the spark plug 10 installed inthe cylinder head H as shown in FIGS. 1( a) and 1(b). In short, thegrounding member 20 is attached onto the spark plug 10, so that thegrounding member 20 is pressed toward the peripheral surface of thehexagonal nut 7 by the resilience of the contact pieces 23. In thisstate, a cap 6 positioned near the high pressure cord C has beendetached. The high pressure cord C extends from the ignition coilconnected to the positive electrode of the battery.

The grounding member 20 can be easily attached to and detached from thespark plug 10 simply by removing the cap 6 of the high pressure cord,without using any special tool or skill.

The grounding strip 22 sticking out of the cylinder head H can be easilyconnected to a grounding wire 25, the end of which is connected to anegative electrode 11 of the battery.

The foregoing structure allows electric charges (generated in the sparkgap G due to discharging) to return to the negative electrode 11 of thebattery via the external electrode 3, spark plug housing 4, groundingmember 20, and grounding wire 25. Even if there is a gap between thespark plug 10 and the cylinder head H, or even if some engine componentsare aged, electric charges can flow without any problem, which iseffective in preventing the discharging performance from being adverselyaffected.

The grounding member 20 prevents lowering of the discharge performanceof the spark plug 10 for reasons which are familiar with the relatedart. Therefore, the spark plug 10 provided with the grounding member 20promotes efficient ignition of air-fuel mixture, and improves thermalefficiency, fuel consumption and torque characteristics of the engine.

FIG. 1( b) shows the spark plug 10 having its head sticking out of thecylinder head H. Alternatively, the spark plug 10 may be embedded in thecylinder head H, and the grounding strip 22 protrudes out of thecylinder head H as shown in FIG. 3.

Referring to FIG. 3, the spark plug 10 is installed deep in the cylinderhead H which has a head cover Hc. A cap 8 includes a body 8 a, and anumbrella 8 b covering an opening 9 of the head cover Hc. The body 8 aextends from the opening 9 to a terminal nut 5 of the spark plug 10.

The grounding strip 22 extends upward from one of the contact pieces 23to the umbrella 8 b through a gap defined by the cylinder head H and thecylinder head cover Hc, and projects out of the cylinder head cover Hc.This structure facilitates a connection between the grounding strip 22and the grounding wire 25. The grounding member 20 can be easilyattached or detached only by removing the cap 8.

The invention is applied to the electric igniter in the embodiment.Alternatively, the invention is also applicable to an electronic igniter(constituted by a long life transistor), which is effective in improvingthe reliability of the igniter and meeting requirements for emissionlimit.

In the embodiment, the grounding member 20 includes the hexagonal top21, which has the six contact pieces 23. The contact pieces 23 extendfrom the six straight sides of the hexagonal top 21, and are engageablewith the side surfaces of the hexagonal nut. Alternatively, a groundingmember 20′ may include three contact pieces 23 which extend from everyother straight side of the hexagonal top 21 as shown in FIG. 4 and FIG.5. The 3-contact-piece structure is advantageous in the followingrespect when compared with the 6-contact-piece structure.

The grounding members 20 of the 3-contact-piece type and those of the6-contact-piece type (shown in FIGS. 2 and 4) are made as follows. Thetops having the contact pieces are punched out of a metal plate.Thereafter, the contact pieces are folded along the six straight sidesof the top. FIG. 6( a) shows the arrangement of the 3-contact-piece typetops on the metal plate while FIG. 6( b) shows the arrangement of the6-contact-piece type tops on the metal plate. In the former case, everyadjacent pairs of the 3-contact-piece type tops can be arranged with asmall gap therebetween, which is effective in saving the metal plate(i.e. resources).

The spring steel is employed in order to make the grounding members 20.Alternatively, stainless steel plates, nonferrous metal such as phosphorbronze, and so on for making springs are also usable.

An electrostatic potential is generated in the combustion chamber withwhich the spark gap G of the spark plug 10 faces when the air-fuelmixture is injected into the combustion chamber or when the combustionchamber is rubbed by the compressed air-fuel mixture. The electrostaticpotential adversely affects discharges generated in the spark plug G.The grounding member 20 can effectively lead such an electrostaticpotential from the combustion chamber to the negative electrode 11 ofthe battery via the external electrode 3 and the housing 4, therebyquickly equalizing potentials at the external electrode 3 and thenegative electrode 11. Therefore, an essential potential difference fordischarging can be applied into the spark gap G, which enables theair-fuel mixture to be efficiently ignited.

Especially, in the case of the electronic type igniter, a predeterminedpotential difference is usually applied between the center and externalelectrodes 2 and 3 under the electronic control. If the electrostaticpotential is generated in the combustion chamber, sometimes thepredetermined potential difference cannot be applied. However, thegrounding member 20 of the invention can speedily equalize the externalelectrode 3 and the negative electrode 11, and lead to effectiveignition of the air-fuel mixture.

The grounding member 20 and grounding strip 22 are preferably made ofbrass, copper, silver or the like having high conductivity. Especially,silver is six times as conductive as iron used for the engine body orthe like. The grounding member 20 made of silver assures several toseveral ten times effective grounding performance compared with agrounding member made of another metal. Further, the silver groundingmember 20 can assure the predetermined potential difference in the sparkplug G several to several ten times as quickly, and enable the air-fuelmixture to be efficiently ignited.

The grounding member can prevent reduction of the dischargingperformance of the spark plug, and improve thermal efficiency at thetime of ignition, and fuel consumption and torque characteristics of theengine.

INDUSTRIAL APPLICABILITY OF THE INVENTION

The grounding member and grounding strip, and connecting method of thegrounding strip of the invention are applicable to engines usinggasoline or liquefied petroleum gas as fuel in vehicles, ships, electricgenerators and so on.

1. A grounding structure for a spark plug which generates electricdischarges between a center electrode and an external electrode and isattached to an engine cylinder head via a screwed part of a spark plughousing near the external electrode, the grounding structure comprising:a grounding member shaped to be engageable with and disengageable from ahexagonal nut of the spark plug housing, and connected to a negativeelectrode of a battery using a grounding wire, wherein the groundingmember includes a hexagonal top whose shape and size are substantiallyidentical to those of the hexagonal nut, the hexagonal top having athrough-hole at a center thereof for the spark plug housing, and contactpieces extending from every two straight sides thereof.
 2. The groundingstructure of claim 1, wherein the grounding member includes contactpieces engageable with a peripheral surface of the hexagonal nut, athrough-hole via which an insulator of the spark plug passes, and agrounding strip extending out of the engine cylinder head.
 3. Agrounding structure for a spark plug which generates electric dischargesbetween a center electrode and an external electrode and is attached toan engine cylinder head via a screwed part of a spark plug housing nearthe external electrode, the grounding structure comprising: a groundingmember shaped to be engageable with and disengageable from a hexagonalnut of the spark plug housing, and connected to a negative electrode ofa battery using a grounding wire, wherein the grounding member includesa hexagonal top which has a shape and size substantially identical tothose of the hexagonal nut, the hexagonal top having a through-hole at acenter thereof for the spark plug housing, and is provided with contactpieces extending from six straight sides thereof.
 4. The groundingstructure of claim 3, wherein the grounding member includes contactpieces engageable with a peripheral surface of the hexagonal nut, athrough-hole via which an insulator of the spark plug passes, and agrounding strip extending out of the engine cylinder head.
 5. A groundwiring device for a spark plug which generates electric dischargesbetween a center electrode and an external electrode and is attached toan engine cylinder head via a screwed part of a spark plug housing nearthe external electrode, the ground wiring device comprising: a groundingmember attached to a spark plug housing and shaped to be engageable withand disengageable from a hexagonal nut of the spark plug housing; and agrounding wire connecting the grounding member to a negative electrodeof a battery, wherein the grounding member includes a hexagonal topwhose shape and size are substantially identical to those of thehexagonal nut, the hexagonal top having through-hole at a center thereoffor the spark plug housing, and contact pieces extending from sixstraight sides thereof.
 6. The grounding wire device of claim 5, whereinthe grounding member includes contact pieces engageable with aperipheral surface of the hexagonal nut, a through-hole via which aninsulator of the spark plug passes, and a grounding strip extending outof the engine cylinder head.
 7. A ground wiring device for a spark plugwhich generates electric discharges between a center electrode and anexternal electrode and is attached to an engine cylinder head via ascrewed part of a spark plug housing near the external electrode, theground wiring device comprising: a grounding member attached to a sparkplug housing and shaped to be engageable with and disengageable from ahexagonal nut of the spark plug housing; and a grounding wire connectingthe grounding member to a negative electrode of a battery, wherein thegrounding member includes a hexagonal top whose shape and size aresubstantially identical to those of the hexagonal nut, the hexagonal tophaving through-hole at a center thereof for the spark plug housing, andthree contact pieces extending from every two straight sides thereof. 8.The grounding wire device of claim 7, wherein the grounding memberincludes contact pieces engageable with a peripheral surface of thehexagonal nut, a through-hole via which an insulator of the spark plugpasses, and a grounding strip extending out of the engine cylinder head.9. A ground wiring method comprising: attaching a grounding member on ahousing of a spark plug which is installed in an engine cylinder head ata screwed part of the spark plug housing near an external housing andwhich generates discharges between a center electrode and an externalelectrode, the grounding member being shaped to be engageable with anddisengageable from a hexagonal nut of the spark plug housing, whereinthe grounding member includes a hexagonal top whose shape and size aresubstantially identical to those of the hexagonal nut, the hexagonal tophaving a through-hole at a center thereof for the spark plug housing,and contact pieces extending from six straight sides thereof; andconnecting the grounding member to a negative electrode of a batteryusing a grounding wire.
 10. A ground wiring method comprising: attachinga grounding member on a housing of a spark plug which is installed in anengine cylinder head at a screwed part of the spark plug housing near anexternal housing and which generates discharges between a centerelectrode and an external electrode, the grounding member being shapedto be engageable with and disengageable from a hexagonal nut of thespark plug housing, wherein the grounding member includes a hexagonaltop whose shape and size are substantially identical to those of thehexagonal nut, the hexagonal top having a through-hole at a centerthereof for the spark plug housing, and contact pieces extending fromevery two straight sides thereof; and connecting the grounding member toa negative electrode of a battery using a grounding wire.